JP7130312B2 - Adhesive tape - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pressure-sensitive adhesive tape that has excellent dimensional stability of thickness when pressurized and can be suitably used for structural adhesion applications such as electronic devices such as smartphones and tablet terminals, vehicle-mounted displays, and TVs.

Portable electronic devices such as smartphones and tablet terminals generally have a structure in which a touch panel and a housing for housing a liquid crystal module are combined. For example, an adhesive tape is used to fix the touch panel and the housing. Furthermore, it is also used to fix the liquid crystal display (LCD) panel and the organic EL panel of the on-vehicle display device and the TV to the housing.

In recent years, these electronic devices are becoming thinner and smaller. Along with this, FPCs (Flexible Printed Circuits), for example, are bent at a sharper angle inside the equipment, and have an internal structure that is always subjected to a strong repulsive force. Further, in order to increase the display area of the LCD, the width of the frame (frame) surrounding the liquid crystal panel is narrowed, that is, so-called frame narrowing is in progress. Therefore, it is necessary to narrow the width of the adhesive tape that secures the housing and the top panel. However, in order to withstand the repulsive force of the FPC and the like from the inside and the impact from the outside, not only the adhesive strength of the pressure-sensitive adhesive layer but also the strength of the substrate is required.

When sticking a narrow adhesive tape to a housing, it is common to carry out a pressurizing process using a press machine. At that time, the pressure applied to the adhesive tape ranges from 0.1 MPa to 5.0 MPa. When the thickness of the adhesive tape varies greatly within that pressure range, the dimensional change of the double-sided adhesive tape 41 causes a gap G between the cover panel 42 and the housing 43, as shown in FIG. is reduced and the original appearance is greatly impaired. Furthermore, when the difference in thickness change of the double-sided adhesive tape 41 due to pressure fluctuation is large, it is difficult to predict the gap G and design the cover panel 42 and the housing 43, and the design itself becomes difficult. Further, when the dimensions of the double-sided adhesive tape 41 are restored with the lapse of time after the pressurizing process, as shown in FIG. There is fear.

By the way, as the base material of this type of pressure-sensitive adhesive tape, it is common to use a polyolefin foam containing polyethylene as a main component or an acrylic foam obtained by adding various fillers to an acrylic resin. For example, Patent Document 1 describes a double-sided pressure-sensitive adhesive tape in which acrylic pressure-sensitive adhesive layers are provided on both sides of a foam base material. Polyolefin resin foams such as polyethylene foams and polypropylene foams are described as specific examples of the foam base material. This foam substrate has a thickness of 50-150 μm and a 30% compressive load of 5-200 kPa.

Patent Literature 2 describes a waterproof double-sided adhesive tape composed of a polyolefin foam base material and an adhesive layer for the purpose of fixing parts of portable electronic devices. The polyolefin foam substrate has a thickness of 70 to 300 μm, a 25% compression strength of 40 to 160 kPa, a tensile strength of 300 to 1500 N/cm ² , an average cell diameter in the thickness direction of 1 to 100 μm, and a flow direction. And the average cell diameter in the width direction is 1.2 to 700 μm.

Patent Document 3 describes an adhesive tape having an adhesive layer on at least one surface of a foam substrate. As specific examples of foam substrates, polyolefin foam substrates such as polyethylene and polypropylene are described. The foam substrate has a thickness of 300 μm or less, an interlayer strength of 6 to 50 N/cm, a 25% compression strength of 30 kPa or more, a tensile strength of 300 N/cm ² or more, and an average cell diameter in the thickness direction of 10 to 100 μm. , the average cell diameter in the machine direction and width direction is 10 to 700 μm.

Patent Document 4 describes a crosslinked polyolefin resin foam sheet having high impact absorption and static resistance. The foamed sheet has an expansion ratio of 1.1 to 2.8 cm ³ /g, an MD average cell diameter of 150 to 250 μm, a CD average cell diameter of 120 to 300 μm, and a thickness of 0.02 to 1.9 mm. The 25% compressive strength is 250-1500 kPa.

Patent Literature 5 describes a pressure-sensitive adhesive sheet that is less likely to deteriorate in performance due to narrowing. The relationship between the 100% modulus M [N/mm ² base material] of this adhesive sheet and the density D [g/cm ³ ] of the foam is 9.0≦(M/D), and the 100% modulus M is 4. higher than .0 [N/mm ² substrate].

Patent Literature 6 describes a fixing member (adhesive tape having a foam base material) for fixing a display portion of a portable electronic device or a display portion protective material to a housing. The average width W [mm] of the narrow portion of the fixing member, the 100% modulus M [N/mm ² base material] of the fixing member, and the thickness Hs [mm] of the foam base material are 0.4/ It satisfies the formula (M×Hs)≦W.

However, in Patent Documents 1 to 6, the change in tape thickness due to the pressurizing process using a press machine and the retention rate of the tape thickness after the pressing process are not sufficiently studied. Furthermore, according to the findings of the present inventors, the conventional physical property evaluation methods described in Patent Documents 1 to 4 cannot sufficiently evaluate whether or not the substrate is suitable for a narrow pressure-sensitive adhesive tape. For example, the "compressive strength" or "compressive load" described in Patent Documents 1 to 4 are merely indices of hardness in the thickness direction, and are not indices of changes in thickness after compression. The "tensile strength", "tensile strength" or "interlaminar strength" described in Patent Documents 2 and 3 are simply the strength when the base material breaks. The "average cell diameter" or "expansion ratio" described in Patent Literatures 3 and 4 is merely an index representing the degree of foaming. The "100% modulus" described in Patent Document 5 simply indicates the tensile strength of the tape. The formula “0.4/(M×Hs)≦W” described in Patent Document 6 is simply a relational expression among tensile strength, tape thickness and tape width.

That is, the conventional physical property evaluation methods described in Patent Documents 1 to 6 are not necessarily suitable to be applied as they are, especially to ultra-thin adhesive tapes. On the other hand, according to the knowledge of the present inventors, in the process of pressing the cover panel and the housing using a press machine using an ultra-thin adhesive tape, the compression deformation rate after pressing is important, and further pressing High load and low displacement in the load-displacement curve are also important for the maintenance rate of the post-time deformation rate and the difficulty of peeling of the cover glass and the housing.

Japanese Patent No. 5947870 Japanese Patent No. 4623198 Japanese Patent No. 5517015 WO2015/046526 Japanese Patent Application Laid-Open No. 2017-2292 Japanese Patent Application Laid-Open No. 2017-2293

The present invention has been made to solve the problems of the prior art as described above. That is, an object of the present invention is to provide an adhesive tape that preferably has an ultra-thin width, has excellent dimensional stability in thickness, and has a small gap G generated in a pressurizing process such as a process of pressing a cover panel and a housing. To provide an adhesive tape which hardly damages the appearance of a product due to the gap G, and hardly causes breakage due to the gap G when the product is dropped.

As a result of intensive studies aimed at achieving the above object, the inventors of the present invention have found that it is very effective to use a substrate exhibiting specific physical properties, and have completed the present invention.

That is, the present invention
An adhesive tape having an adhesive layer on one or both sides of a substrate,
The base material is made of a polyolefin resin composition containing an ethylene-vinyl acetate copolymer and other polyolefin resin, and has an expansion ratio of 1.1 to 3.5 times and an expansion ratio of 0.3 mm to 2.0 mm. It is a foam that eliminates voids of size,
The base material contains 30% by mass or more of an ethylene-vinyl acetate copolymer,
The pressure-sensitive adhesive layer has a thickness of 5 to 100 μm,
The adhesive layer comprises an acrylic adhesive composition containing a (meth)acrylic ester copolymer , a cross-linking agent and a silane coupling agent , and a monomer constituting the (meth)acrylic ester copolymer the body contains (meth)acrylic acid alkyl ester, a carboxyl group-containing monomer and a hydroxyl group-containing monomer,
The pressure-sensitive adhesive layer has a crosslinked structure formed by blending the (meth)acrylic acid ester copolymer with the crosslinking agent,
The pressure-sensitive adhesive tape is characterized by having a compressive deformation rate during adhesion of 0 to -10% when the pressure-sensitive adhesive tape is compressed within a range of 0.3 to 5.0 MPa.

In the applications mentioned above, polyethylene-based foam substrates containing closed cells are generally used. Comparing a foamed base material with high compressive strength and a foamed base material with low compressive strength, the foamed base material with low compressive strength deforms more under pressure. Moreover, even a foamed base material with high compressive strength may undergo a large change from its original thickness due to plastic deformation when pressurized with a very high pressure of 0.1 to 5.0 MPa. On the other hand, the pressure-sensitive adhesive tape of the present invention has excellent dimensional stability of thickness, and the gap G generated in the pressure process such as the process of pressing the cover panel and the housing is small, and the gap G does not impair the appearance of the product. Moreover, it is difficult for the product to be damaged due to the gap G when the product is dropped. Therefore, it is useful for various applications in fields where such properties are required.

FIG. 4 is a schematic cross-sectional view for explaining a bending moment measuring method of an example. 4 is a graph for explaining a master curve obtained by dynamic viscoelasticity measurement in Examples. FIG. 4 is a schematic cross-sectional view for explaining a method for measuring a load-displacement curve in an example. FIG. 10 is a schematic cross-sectional view for explaining a problem in which a gap is generated between the cover panel and the housing in the prior art;

<Base material>
The base material used in the present invention may be a base material having a compression deformation rate during adhesion of 0 to -10% when the pressure-sensitive adhesive tape having this base material is compressed within the range of 0.3 to 5.0 MPa. , the type of which is not limited. For example, a substrate containing 30% by mass or more of an ethylene-vinyl acetate copolymer and having a tensile modulus of elasticity of 30 N/mm ² or more is preferable.

The substrate is preferably made of a polyolefin resin composition containing an ethylene-vinyl acetate copolymer and another polyolefin resin. Other polyolefin-based resins include, for example, polyethylene-based resins, polypropylene-based resins, or mixtures thereof. Linear low density polyethylene (LLDPE) and ethylene propylene rubber (EPDM) are particularly preferred.

The resin composition that constitutes the substrate can be produced by a known method. For example, a resin composition that constitutes the substrate can be obtained by irradiating a resin composition containing 30% by mass or more of an ethylene-vinyl acetate copolymer and another polyolefin resin with an electron beam to crosslink the resin composition. Foaming may be performed simultaneously with this cross-linking or at a different time.

The resin composition constituting the base material may contain other additives as long as the effects of the present invention are not impaired. Specific examples thereof include extenders, cross-linking agents, antioxidants, stabilizers, elastomers and coupling agents. Furthermore, light shielding fillers and pigments may be included. Specific examples of light-shielding fillers include carbon black, carbon nanotubes, and black inorganic fillers. Specific examples of pigments include carbon black, aniline black, acetylene black, and ketjen black.

The width of the substrate is preferably 0.4-2.0 mm, more preferably 0.45-1.5 mm, particularly preferably 0.6-1.2 mm. The thickness of the substrate is preferably 0.05-1.0 mm, more preferably 0.05-0.4 mm.

The base material is a foam, and its expansion ratio is preferably 1.1 to 3.5 times, more preferably 1.5 to 3.0 times. The cell shape of the foam is preferably spherical. Furthermore, it is preferable that the base material contains closed cells from the viewpoint of properties such as waterproofness. In the present invention, it is preferable to use a substrate controlled so as to exclude void diameters of 0.3 mm to 2.0 mm contained in the substrate, and more preferably to exclude sizes of 0.4 mm to 1.4 mm. It is desirable that the base material is managed as follows. Moreover, it is preferable that the base material does not contain voids (defective cells) whose size is significantly different from the controlled cell diameter.

<Adhesive layer>
The pressure-sensitive adhesive layer used in the present invention is not particularly limited. As the adhesive composition constituting the adhesive layer, various known adhesive compositions such as acrylic, rubber, silicone, and urethane can be used. Among them, an acrylic pressure-sensitive adhesive composition is preferable from the viewpoint of heat resistance, impact resistance, adhesive strength, and waterproofness, and the pressure-sensitive adhesive layer preferably contains a (meth)acrylic acid ester copolymer.

The constituent components of the acrylic pressure-sensitive adhesive composition are not particularly limited. An acrylic pressure-sensitive adhesive composition usually contains an acrylic polymer obtained by using a (meth)acrylic acid alkyl ester having a linear or branched alkyl group as a main monomer component. Specific examples of (meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, (meth) ) isobutyl acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate , octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, (meth)acrylic acid Isodecyl, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate , octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. Among them, (meth)acrylic acid C2-14 alkyl ester is preferable, and (meth)acrylic acid C2-10 alkyl ester is more preferable.

As a monomer constituting the acrylic polymer, it is preferable to use an appropriate amount of (meth)acrylic acid C1-3 alkyl ester such as methyl acrylate. This (meth)acrylic acid C1-3 alkyl ester improves narrow-frame adhesion, load resistance, processability, and narrow-frame wet heat load resistance. The amount of (meth)acrylic acid C1-3 alkyl ester is preferably 2% by mass or more, more preferably 3 to 15% by mass, based on 100% by mass of the acrylic polymer. The lower limit of this range is significant in terms of narrow-frame adhesion, load resistance, workability, and narrow-frame wet heat load resistance. Moreover, the upper limit value is significant in terms of the initial sticking property of the adhesive tape when performing various evaluations.

As monomers constituting the acrylic polymer, various copolymerizable monomers such as polar group-containing monomers and polyfunctional monomers may be used in order to improve adhesion or cohesion. Two or more copolymerizable monomers may be used in combination. Furthermore, a cross-linking structure may be formed by blending a cross-linking agent capable of reacting with the polar group-containing monomer or the polyfunctional monomer. Additives such as silane coupling agents and antioxidants may also be blended.

Specific examples of polar group-containing monomers include carboxyl group-containing monomers such as (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid, or their anhydrides (maleic anhydride, etc.). ; hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxyl group-containing monomers such as hydroxyalkyl (meth) acrylate such as hydroxybutyl (meth) acrylate; (meth) acrylamide, N, N- Amide group-containing monomers such as dimethyl (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide; (meth) aminoethyl acrylate, (meth ) amino group-containing monomers such as dimethylaminoethyl acrylate and t-butylaminoethyl (meth)acrylate; glycidyl group-containing monomers such as glycidyl (meth)acrylate and methylglycidyl (meth)acrylate; ( meth) cyano group-containing monomers such as acrylonitrile; heterocycle-containing vinyl monomers such as N-vinylimidazole and N-vinyloxazole; alkoxyalkyl (meth)acrylate monomers such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate; vinyl sulfonic acid group-containing monomers such as sodium sulfonate; phosphoric acid group-containing monomers such as 2-hydroxyethyl acryloyl phosphate; imide group-containing monomers such as cyclohexylmaleimide and isopropylmaleimide; 2-methacryloyloxyethyl isocyanate and isocyanate group-containing monomers; Among them, carboxyl group-containing monomers such as acrylic acid and hydroxyl group-containing monomers such as hydroxybutyl acrylate are preferred.

A carboxyl group-containing monomer improves properties such as narrow-frame adhesion, load resistance, workability, and narrow-frame wet heat load resistance. The amount of the carboxyl group-containing monomer is preferably 10 to 20% by mass, more preferably 10 to 12% by mass, based on 100% by mass of the acrylic polymer. The lower limits of these ranges are significant in terms of tight-frame adhesion, load resistance, workability, and narrow-frame wet heat load resistance. Moreover, the upper limit value is significant in terms of the initial sticking property of the adhesive tape when performing various evaluations.

A hydroxyl group-containing monomer improves properties such as narrow-frame adhesion, load resistance, workability, and narrow-frame wet heat load resistance. The amount of the hydroxyl group-containing monomer is preferably 0.01 to 2.0% by mass, more preferably 0.05 to 0.15% by mass, based on 100% by mass of the acrylic polymer. The upper limit of these ranges is to suppress the change over time of the adhesive tape in a heated/moist heat atmosphere, and to maintain sufficient narrow frame adhesion, load resistance, workability, narrow frame moist heat load resistance, etc. is meaningful.

The thickness of the adhesive layer is preferably 5-200 μm, more preferably 10-100 μm.

The pressure-sensitive adhesive layer can be formed, for example, by subjecting the pressure-sensitive adhesive composition to a cross-linking reaction. That is, the pressure-sensitive adhesive composition can be coated on a substrate and crosslinked by heating to form a pressure-sensitive adhesive layer on the substrate. Alternatively, the adhesive composition may be coated on a release paper or other film, crosslinked by heating to form an adhesive layer, and the adhesive layer may be attached to one or both sides of a substrate. Coating devices such as roll coaters, die coaters, and lip coaters can be used to apply the adhesive composition. When heating after coating, the solvent in the pressure-sensitive adhesive composition can be removed together with the cross-linking reaction by heating. In addition, it is preferable that the adhesive layer does not contain a tackifying resin.

<Adhesive tape>
The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer on one side or both sides of the substrate. The pressure-sensitive adhesive layer may be formed only on one side of the substrate, but is preferably formed on both sides to form a double-sided pressure-sensitive adhesive tape.

When the pressure-sensitive adhesive tape of the present invention is compressed within the range of 0.3 to 5.0 MPa, the compression deformation ratio during adhesion is 0 to -10%, preferably 0 to -8%. In addition, the rate of retention of compression deformation during bonding after compression within the range of 0.3 to 5.0 MPa is preferably within ±3%, more preferably within ±2%.

The pressure-sensitive adhesive tape of the present invention preferably has a minimum loss tangent in the range of 50 to 100° C. and a difference between the minimum loss tangent and the 150° C. loss tangent of 1.5×10 ⁻¹ or less. A minimum loss tangent within the range of 50 to 100° C. is significant in terms of dynamic adhesive strength and peel displacement. In addition, the difference between the lowest loss tangent and the 150° C. loss tangent of 1.5×10 ⁻¹ or less is significant in terms of compression deformation rate during bonding, dynamic adhesive strength, and peel displacement.

The storage modulus change point α of the pressure-sensitive adhesive tape of the present invention is preferably 100° C. or higher. Further, in the load-displacement curve when the substrate is pulled at 1 mm/min, it is preferable that there is no delamination of the base material, the maximum load value is 40 N/cm ² or more, and the peel displacement is 2.0 mm or less.

The pressure-sensitive adhesive tape of the present invention preferably has a 40% compression strength of 2 MPa or more, more preferably 2 to 5 MPa, as measured by compression strength measurement according to JIS K-7181.

Specific measurement conditions for each physical property value described above are as described in Examples described later.

The pressure-sensitive adhesive tape of the present invention can be pressed at a very high pressure of 0.1-5.0 MPa. In particular, due to its dimensional stability, it is suitable for narrow adhesive tapes. Therefore, it is useful for various applications in fields where such properties are required. Specifically, it is very useful as a pressure-sensitive adhesive tape for bonding structures and a pressure-sensitive adhesive tape for bonding electronic devices.

EXAMPLES The present invention will now be described in more detail with reference to examples and comparative examples. In the following description, "parts" means parts by mass, and "%" means % by mass.

<Preparation Examples 1 to 3 of adhesive layer>
A reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet tube was charged with the components (A1) to (A5) in the amounts (%) shown in Table 1, ethyl acetate, and n-dodecanethiol as a chain transfer agent. And 0.1 part of lauryl peroxide was charged as a peroxide radical polymerization initiator. Nitrogen gas was sealed in the reactor, and the polymerization reaction was carried out at 68° C. for 3 hours under a nitrogen gas stream with stirring, and then at 78° C. for 3 hours. It was then cooled to room temperature and ethyl acetate was added. As a result, an acrylic copolymer (A) having a solid concentration of 30% was obtained.

Table 1 shows the weight average molecular weight (Mw) and theoretical Tg of each acrylic copolymer. This weight average molecular weight (Mw) is a value obtained by measuring the molecular weight of the acrylic copolymer in terms of standard polystyrene by the GPC method using the following measuring apparatus and conditions.
・ Apparatus: LC-2000 series (manufactured by JASCO Corporation)
・Column: Shodex KF-806M x 2, Shodex KF-802 x 1 ・Eluent: Tetrahydrofuran (THF)
・Flow rate: 1.0 mL/min ・Column temperature: 40°C
・Injection volume: 100 μL
・Detector: Refractometer (RI)
・Measurement sample: An acrylic polymer was dissolved in THF to prepare a solution having an acrylic polymer concentration of 0.5% by mass, and dust was removed by filtration through a filter.

The theoretical Tg is a value calculated by the FOX formula.

Abbreviations in Table 1 are as follows.
"MA": methyl acrylate "2-EHA": 2-ethylhexyl acrylate "BA": n-butyl acrylate "AA": acrylic acid "4-HBA": 4-hydroxybutyl acrylate "Vac": vinyl acetate

Then, to 100 parts of the solid content of each acrylic copolymer (A), 0.5% of an isocyanate cross-linking agent (Coronate (registered trademark) L-45E, 45% solution) manufactured by Tosoh Corporation is added as a cross-linking agent (B). 04 parts, 0.1 part of silane coupling agent (trade name KBM-403) manufactured by Shin-Etsu Chemical Co., Ltd. as silane coupling agent (C), antioxidant (D) BASF antioxidant (Irganox (registered trademark) 1010) was added and mixed to prepare an adhesive composition. Next, the solvent was removed and dried at 110° C., and cross-linking was allowed to occur, and the pressure-sensitive adhesive composition was applied onto silicone-treated release paper so as to have a thickness of 0.075 mm after drying.

<Example 1>
First, a base material made of polyethylene (PE) foam containing ethylene-vinyl acetate copolymer (thickness = 0.15 mm, tensile modulus = 46.1 N/mm ² , bending moment (MD direction) = 16 gf/cm , (TD direction) = 17 gf/cm, expansion ratio = 1.9, density = 544 kg/m ³ ) and no voids (defective cells) were prepared. Then, both sides of this base material were subjected to corona discharge treatment, and the adhesive layer on the release paper obtained in Production Example 1 was attached to both sides of the base material, and cured at 40° C. for 3 days to obtain a double-sided adhesive tape. .

<Examples 2 and 3>
A double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive layers obtained in Production Examples 2 and 3 were used as the pressure-sensitive adhesive layer.

<Comparative Example 1>
As a substrate, a PE-based foam (thickness = 0.2 mm, tensile modulus = 21.0 N/mm ² , bending moment (MD direction) = 3 gf/cm, (TD direction) = 4 gf/cm, expansion ratio = 3, density = 330 kg/m ³ ), and a double-sided pressure-sensitive adhesive tape was obtained in the same manner as in Example 1 except that the thickness of the pressure-sensitive adhesive layer after drying was 0.05 mm.

<Comparative Example 2>
As a base material, a PE-based foam (thickness = 0.15 mm, tensile modulus = 23.7 N/mm ² , bending moment (MD direction) = 7 gf/cm, (TD direction) = 8 gf/cm, expansion ratio = 1.8, density = 560 kg/m ³ ) to obtain a double-sided pressure-sensitive adhesive tape in the same manner as in Example 1.

The tensile elastic modulus of the base material and the bending moment of the base material and the adhesive tape in Examples and Comparative Examples are values measured by the following methods. Each measured value is shown in Table 2.

(tensile modulus)
The base material was cut into a strip having a width (W) of 10 mm and a length of 70 mm (the long side is in the MD direction), and this was used as a test piece. Then, the thickness was measured with a 1/100 dial gauge (N=5), the average value of 5 points was taken as the thickness (t), and the cross-sectional area (S) of the test piece was obtained from the following formula.
Cross-sectional area S (mm ² ) = t x W
t: thickness (mm)
W: Width (mm)

Based on JIS K7161 2014, set the chuck interval (L) of a commercially available tensile tester (manufactured by Toyo Seiki Seisakusho, device name Strograph V-10C, full scale 50N) to 20 mm, and chuck the upper and lower ends of the test piece. did. Then, it was pulled at a tensile speed of 10 mm/min to obtain a tensile load-displacement curve. A linear equation was determined from the tensile load with a displacement of 0.05 mm and 0.25 mm in the resulting tensile load-displacement curve. A displacement x (mm) at a tensile load F=10 N was obtained from the obtained linear equation, and a tensile elastic modulus, which is an index of the stiffness of the base material, was obtained from the following equation.
Tensile modulus (N/mm ² ) = (F/S)/(x/L)
F: Tensile load = 10 (N)
S: cross-sectional area (mm ² )
x: Displacement (mm) when tensile load = 10 N
L: Chuck interval = 20 (mm)

In addition, each linear equation and tensile elastic modulus are as follows.
Examples 1 to 3: Linear formula y = 3.6667x + 0.0767, tensile modulus 46.1 N / mm ²
Comparative Example 1: Linear formula y=1.2632x-0.0432, tensile modulus 21.0 N/mm ²
Comparative Example 2: Linear formula y = 2.1026x + 0.1349, tensile modulus 23.7 N / mm ²

(bending moment)
A substrate (or double-sided adhesive tape) 11 was cut into strips having a width of 38 mm and a length of 50 mm, which were used as test pieces. The obtained test piece was sandwiched between four terminals 12 as shown in FIG. Then, based on JIS P8125, a commercially available Taber stiffness tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.) was installed at the part that operates during the test, a vertical 10 g weight was attached to the pendulum, and the bending speed was 3 ° / sec and the bending angle was 15. Read the scale in ° and use this as the measured value. Then, the measured values were substituted into the following formulas to calculate bending moments (M) in the MD and TD directions.
Bending moment (gf/cm) = 38.0 nk/w
n: Reading on the scale (1 when the weight is 10g)
k: Moment per scale (gf/cm)
w: Width of test piece

<Evaluation test>
The double-sided pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples were evaluated by the following methods. The results are shown in Tables 3-6.

(Compressive deformation rate during adhesion)
The double-sided pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples were processed into squares of 10 mm×10 mm, sandwiched from both sides by white PET films having a thickness of 75 μm, and pressed with a press. At this time, the actual pressure applied to the adhesive tape was 0.3 MPa, 0.5 MPa, 1.0 MPa, 1.5 MPa, 2.0 MPa, 4.0 MPa, and 5.0 MPa. Within 5 minutes after this pressurization, the thickness of the tape was measured by observing the cross section of the tape with a laser microscope VK-X260 manufactured by Keyence Corporation. Then, the compressive deformation rate during adhesion was calculated by the following formula.
(Compressive deformation rate during adhesion) = (thickness before pressure - thickness after pressure) / (thickness before pressure) x 100 [%]

(Maintenance rate of compressive deformation rate during bonding)
Each double-faced pressure-sensitive adhesive tape whose compressive deformation rate during adhesion was measured was stored at 23° C. and 50% RH for 24 hours. Then, the thickness of the tape was measured by observing the cross section of the tape with a laser microscope VK-X260 manufactured by Keyence Corporation. Then, the retention rate of the compressive deformation rate during bonding was calculated by the following formula.
(Maintenance rate of compression deformation rate during adhesion) = (thickness when stored for 24 hours after pressurization - thickness immediately after pressurization) / (thickness immediately after pressurization) x 100 [%]

(Storage modulus change point α, lowest loss tangent, 150°C loss tangent)
The double-sided adhesive tapes obtained in Examples and Comparative Examples were superimposed to a thickness of 2 mm, and a dynamic viscoelasticity measuring device (TA Instruments Japan Co., Ltd., RDA-III) was used to measure the jig. The dynamic viscoelasticity was measured under the conditions of a parallel plate of φ8 mm, a frequency of 10 Hz, a measurement temperature of -50° C. to 150° C., and a heating rate of 10° C./min to obtain a master curve as shown in FIG. α, lowest loss tangent, 150° C. loss tangent were obtained.

(maximum load and displacement of load-displacement curve)
The double-sided pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples were cut into a size of 10 mm×10 mm, and the release paper on one side was peeled off. Then, as shown in FIG. 3, a T-shaped jig 32 made of SUS304 was pasted with a double-sided adhesive tape 31, and then the other release paper was peeled off. pasted together. A pressure of 0.5 MPa was applied for 10 seconds, followed by pulling upward at a rate of 1 mm/min in an atmosphere of 23° C. and 50% RH within 5 minutes to obtain a load-displacement curve. From the resulting curve, the maximum load and the displacement mm when the bonded portion was peeled off were measured.

(40% and 50% compressive strength)
The double-sided adhesive tapes obtained in Examples and Comparative Examples were superimposed to a thickness of 12 mm, and a compressive strength measuring device (manufactured by Shimadzu Corporation, AG-20kNX) was used, and measurement (analysis) software was Trapezium X. , under the condition of single measurement mode, 0 to 50% compressive strength was measured according to JIS K-7181, a master curve was created, and 40% and 50% compressive strengths were obtained.

<Evaluation>
As is clear from the evaluation results in Tables 3 to 6, the double-sided pressure-sensitive adhesive tapes of Examples 1 to 3 were excellent in all properties regardless of 40% and 50% compressive strength.

Since the double-faced adhesive tapes of Comparative Examples 1 and 2 have a large compressive deformation ratio during adhesion, the cover panel 42 and the housing are separated from each other by a dimensional change in the thickness of the double-sided adhesive tape 41 in the pressure process, as shown in FIG. 4A, for example. The gap G between the bodies 43 becomes large, the sense of unity is lowered, and there is a possibility that the original appearance is greatly damaged. In addition, since the double-sided adhesive tapes of Comparative Examples 1 and 2 have a large difference in compression deformation rate during adhesion at each pressure of 0.1 MPa to 5.0 MPa, the cover panel 42 and the housing 43 are designed by estimating the gap G. is difficult.

Since the double-sided adhesive tape of Comparative Example 1 has a large rate of maintaining the compressive deformation rate during adhesion (the deformation cannot be maintained), even if the gap G is predicted and the cover panel 42 and the housing 43 are designed, for example, FIG. ), the cover panel 42 may protrude from the housing 43 .

Since the double-sided pressure-sensitive adhesive tapes of Comparative Examples 1 and 2 have a storage elastic modulus change point α of 100° C. or less, it is more difficult to predict the gap G and design the cover panel 42 and the housing 43 . Further, the double-sided pressure-sensitive adhesive tape of Comparative Example 1 has a low maximum load in the load-displacement curve due to tensile force, so it tends to be easily peeled off by tensile force.

Since the pressure-sensitive adhesive tape of the present invention has a small compressive deformation rate during adhesion regardless of the compressive strength of 40% and 50%, it can be used in various fields where such properties are required. In particular, it can be suitably used for electronic devices such as smartphones and tablet terminals. Specifically, it can be used for fixing a housing and a cover panel, fixing a vehicle-mounted LCD and a housing, and the like.

11 base material (or double-sided adhesive tape)
12 terminal 31 double-sided adhesive tape 32 SUS304 T-shaped jig 33 glass plate 41 double-sided adhesive tape 42 cover panel 43 housing G gap

Claims (13)

An adhesive tape having an adhesive layer on one or both sides of a substrate,
The base material is made of a polyolefin resin composition containing an ethylene-vinyl acetate copolymer and other polyolefin resin, and has an expansion ratio of 1.1 to 3.5 times and an expansion ratio of 0.3 mm to 2.0 mm. It is a foam that eliminates voids of size,
The base material contains 30% by mass or more of an ethylene-vinyl acetate copolymer,
The thickness of the adhesive layer is 5 to100μm,
The pressure-sensitive adhesive layer is a (meth) acrylic acid ester copolymer,cross-linking agentand silane coupling agentwherein the monomers constituting the (meth)acrylic acid ester copolymer are (meth)acrylic acid alkyl ester, a carboxyl group-containing monomer and a hydroxyl group-containing monomer including
The pressure-sensitive adhesive layer has a crosslinked structure formed by blending the (meth)acrylic acid ester copolymer with the crosslinking agent,
When the pressure-sensitive adhesive tape is compressed within the range of 0.3 to 5.0 MPa, the compression deformation rate at the time of adhesion is 0 to -10%.
An adhesive tape characterized by: 2. The pressure-sensitive adhesive tape according to claim 1, wherein the rate of retention of compression deformation during adhesion after compression within the range of 0.3 to 5.0 MPa is within ±3%. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the minimum loss tangent is in the range of 50 to 100° C., and the difference between the minimum loss tangent and the 150° C. loss tangent is 1.5×10 ⁻¹ or less. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the storage modulus change point α is 100° C. or higher. 5. The pressure-sensitive adhesive tape according to claim 1, wherein the base material contains spherical air bubbles. 2. The pressure-sensitive adhesive tape according to claim 1, wherein the load-displacement curve when pulled at 1 mm/min shows no interlaminar breakage of the base material, a maximum load value of 40 N/cm ² or more, and a peel displacement of 2.0 mm or less. . 2. The pressure-sensitive adhesive tape according to claim 1, which has a 40% compression strength of 2 MPa or more as measured by compression strength measurement according to JIS K-7181. 2. The pressure-sensitive adhesive tape according to claim 1 , wherein the other polyolefin resin is a polyethylene resin, a polypropylene resin, or a mixture thereof. 2. The pressure-sensitive adhesive tape according to claim 1, wherein said pressure-sensitive adhesive layer does not contain a tackifying resin. The pressure-sensitive adhesive tape according to claim 1, wherein the base material has a tensile modulus of elasticity of 30 N/mm ² or more as measured according to JIS K7161 2014. 2. The pressure-sensitive adhesive tape of claim 1, wherein the substrate contains closed cells. The pressure-sensitive adhesive tape of claim 1, which is a structure-bonding pressure-sensitive adhesive tape. The adhesive tape according to claim 1, which is an adhesive tape for bonding electronic equipment.

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